In semiconductor manufacturing technology, a mask (also referred to as a photomask or reticle) is used by a photolithography system to expose a pattern onto a substrate. The pattern can include many small or tight features, which are defined by a critical dimension (CD). However, as critical dimensions become smaller, for example from 45 nm to 32 nm, the time required to expose the pattern on the substrate becomes longer. For example, it is not unusual to require 5 to 10 hours to expose a mask pattern on a substrate.
As exposure times become longer, certain problems can arise. One such problem is referred to as a blank photoresist vacuum effect. The blank photoresist vacuum effect refers to variations in the sensitivity of the photo-sensitive material (e.g., the resist) used on the substrate that occur during long exposure times. These variations in sensitivity can cause shifting of critical dimensions between local areas of the substrate. The shifting of critical dimensions between local areas is referred to as a CD side-to-side tilting error. The CD side-to-side tilting error in turn affects the CD uniformity of the underlying substrate.
A need exists for a method and system that reduces the CD side-to-side tilting error, which will in turn improve the CD uniformity of the patterned substrate.